The microphone was set to
0db according to
alsamixer. I had trouble seeing how to set to a sensible level.
Then I found how to set it but, but the microphone is still not working.
Try installing pulseAudio volume controller:
Then start it from the HUD display and go to the input devices tab, select the "microphone" option from the drop-down, its "Internal microphone" by default, which most probably not the one attached somewhere on your screen, with a small opening. this worked on my acer aspire one when i wanted to use audacity.